Runx2 is preferentially expressed in metastatic prostate cancer cells, but not in non-metastatic cells, promotes aggressive tumor behavior and induces a spectrum of cancer-related genes. Therefore, Project 3 will test the hypothesis that prostate cancer progression is highly Runx2-dependent and this signaling network provides a viable target for translational approaches to inhibit prostate tumorigenesis and metastasis. State-of-the-art experimental strategies will be employed including prostate specific genomics, in vivo bioimaging using luciferase transgenes, and RNA interference using Runx2 shRNA in prostate and metastatic bone tumors to mechanistically characterize Runx2-mediated control of prostate cancer tumorigenesis and metastasis as well as to establish therapeutic potential for Runx 2 inhibition. Experiments in Aim 1 will characterize mechanisms in vitro by which Runx2 contributes to prostate cancer cell growth and metastatic properties. This will involve analysis of Runx2 expression and function in the regulation of cell survival (in collaboration with Project 1). adhesion and invasion (in collaboration with Project 2\ of androgen dependent and -independent model prostate cancer cells. Expression profiling and bioinformatic analysis will identify Runx2-related pathways induced in these settings, and validation studies will focus on TGPB, integrin, and Src signaling pathways activated by Runx2. Experiments in Aim 2 will examine in vivo mechanisms by which Runx2 contributes to prostate cancer progression and metastatic bone disease. The hypothesis that Runx2-dependent gene expression is differentially modulated in distinct prostate and bone microenvironments will be investigated in orthotopic models. Analysis of bone lesions (osteolytic versus osteoblastic), modulation of tumor growth, and elucidation of gene pathways suppressed or activated by manipulating Runx2 levels will be determined by molecular imaging, laser-capture microdissection, quantitative histopathology and biochemical characterization of TGPB/SMAD or Src/WW signaling. Aim 3 will investigate the tumorigenic properties of Runx2 in TRAMP mice and the therapeutic potential of Runx2 depletion (by shRNA Runx2) in both the TRAMP mouse and in pre-formed orthotopic prostate and bone tumors in the SCID mouse. This study will provide mechanistic insight into Runx2 control of signaling pathways mediating growth of primary prostate tumors and prostate tumors that have metastasized to bone. A basis will be provided for pre-clinical evaluation of targeting Runx2 by shRNA inhibition in prostate cancer cells before acquisition of metastatic properties.